A layer system of this type has a substrate with a metal alloy based on nickel or cobalt. Products of this type are used in particular as a component of a gas turbine, in particular as gas turbine blades or vanes or heat shields. The components are exposed to a hot-gas stream of aggressive combustion gases. Therefore, they have to be able to withstand high thermal stresses. Furthermore, it is necessary for these components to be resistant to oxidation and corrosion. Moreover, mechanical demands are imposed in particular on moving components, e.g. gas turbine blades or vanes, but also on static components. The power and efficiency of a gas turbine in which components that can be exposed to hot gas are used increase as the operating temperature rises. Therefore, constant attempts have been made to achieve a higher gas turbine performance by improving the coating system.
To achieve a high efficiency and a high power, components of the gas turbines which are particularly exposed to the high temperatures are coated with a ceramic material. This acts as a thermal barrier coating between the hot-gas stream and the metallic substrate.
The metallic base body is protected from the aggressive hot-gas stream by coatings. Modern components generally have a plurality of coatings, which each perform specific tasks. Therefore, a multilayer system is employed.
EP 0 944 746 B1 discloses the use of pyrochlores as a thermal barrier coating.
However, it is not only good thermal barrier properties which are required for a material to be used as a thermal barrier coating, but also a good bonding to the substrate.
EP 0 992 603 A1 discloses a thermal barrier coating system made up of gadolinium oxide and zirconium oxide, which is not supposed to have a pyrochlore structure.